A 300ml tube is a 10 0z tube (also is a 18 cubic inch tube).
These are all volume measures.
This tube should fill about 12 ft of the crack size you describe IF
there is no leakage.
If the crack allows the material to leak away you could be filling
for a LONG time.
SIKA makes a self leveling crack filler material but it is very runny
and doesn't work well if the floor has more than a degree or so of
I've filled crack as big as 1" wide x 1" deep x 1' long (way beyond
the stated label limits as an experiment as to how the stuff works)
On this really big crack, foam backer rod didn't seal well so I flowed
fine sand into the crack.
I washed it in with a light stream of water. I kept the sand well
below the surface.
The crack in your situatuon is probably too small to use the sand
check out the self leveling sealant